[Python-Dev] __str__ vs. __unicode__

[Walter Dörwald]

Brett C. wrote:

> Walter Dörwald wrote:
> 
>> M.-A. Lemburg wrote:
>>
>>> [...]
>>> I don't have a clear picture of what the consensus currently
>>> looks like :-)
>>>
>>> If we're going for for a solution that implements the hook
>>> awareness for all __<typename>__ hooks, I'd be +1 on that.
>>> If we only touch the __unicode__ case, we'd only be created
>>> yet another special case. I'd vote -0 on that.
>>> [...]
>>
>> Here's the patch that implements this for int/long/float/unicode:
>> http://www.python.org/sf/1109424
> 
> Any movement on this?  +1 for making things work like str; if a subclass 
> overrides __str__ it should use that method.  If correctness of what is
> returned is a worry then a check could be tossed in before the value is 
> returned.

It already works that way:

Python 2.5a0 (#1, Feb 24 2005, 16:25:04)
[GCC 2.96 20000731 (Red Hat Linux 7.3 2.96-113)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
 >>> class u(unicode):
...  def __unicode__(self): return 42
...
 >>> unicode(u("foo"))
Traceback (most recent call last):
   File "<stdin>", line 1, in ?
TypeError: coercing to Unicode: need string or buffer, int found
 >>> class i(int):
...  def __int__(self): return "foo"
...
 >>> int(i(42))
Traceback (most recent call last):
   File "<stdin>", line 1, in ?
TypeError: __int__ returned non-int (type str)
 >>> class l(long):
...  def __long__(self): return "foo"
...
 >>> long(l(42))
Traceback (most recent call last):
   File "<stdin>", line 1, in ?
TypeError: __long__ returned non-long (type str)
 >>> class f(float):
...  def __float__(self): return "foo"
...
 >>> float(f(42))
Traceback (most recent call last):
   File "<stdin>", line 1, in ?
TypeError: __float__ returned non-float (type str)

Bye,
    Walter Dörwald